1. Field of the Invention
The subject invention is directed to cardiac leads, and more particularly, to an implantable defibrillation lead that includes one or more articulated shocking coils for delivering electrical energy to cardiac tissue.
2. Background of the Related Art
An implantable cardioverter defibrillator (ICD) is a device that is implanted in the chest to monitor for and, if necessary, correct episodes of certain types of abnormal heart rhythms (arrhythmia). One example of such an arrhythmia is an exceptionally fast heartbeat (ventricular tachycardia), in response to which an ICD will supply a small amount of electrical energy to stimulate the heart and restore a normal rhythm (i.e., the ICD performs “anti-tachycardia pacing”). This act of converting one heart rhythm to another is called “cardioversion”. In more extreme cases, the heartbeat may be so rapid that it amounts to quivering rather than beating; this is called “ventricular fibrillation.” To remedy this potentially fatal condition, an ICD performs “defibrillation” by administering a relatively large amount of electrical energy to the heart to restore a normal heartbeat.
In order to perform the above functions, the ICD includes an electrical signal generator and an implantable defibrillation lead for operatively connecting the generator to the heart. The signal generator is contained within a housing that is implanted in the chest of a patient during a surgical procedure. The implantable defibrillation lead is passed through a blood vessel until the distal end of the lead engages the inner surface of the heart. The other (proximal) end connects to the signal generator. In general, these leads include one or more elongated shocking coils located proximate to the distal end and designed to deliver electrical energy from the generator to cardiac tissue upon demand. Typically, such leads further include one or more sensors located proximally to the distal end, which detect the onset of episodes of arrhythmia.
Typically, a shocking coil is formed from one or more conductive wires that are helically wound about a continuous cylindrical section of the lead body. Such coils provide a large surface area for contacting the heart, thereby efficiently delivering energy to the heart when needed. However, one significant disadvantage seen with these prior art coils is that they have a tendency to buckle when the lead body is urged through blood vessels en route to the heart. This buckling stems from the fact that the vessels through which the lead must travel are sinuous, and the varying shape of the vessels provides along their length varying levels of resistance to further forward movement of the lead. As the physician urges the lead through the vessel, the shocking coil may buckle before it can navigate the required turns.
When a shocking coil buckles, it tends to become wider or increase in diameter in a localized area. This decreases the effectiveness of the coil in delivering energy to the heart and can cause localized scaring in adjacent tissue. In addition, such buckling of the coil leads to a local increase in the spacing of adjacent turns of the coil, thereby allowing detrimental tissue ingrowth into the coil. It would be beneficial, therefore, to provide a defibrillation lead having a shocking coil that is not susceptible to buckling during implantation.